Display device

ABSTRACT

A display device includes: a substrate; a display element on the substrate; a capping layer on the display element; an optical layer on the capping layer, and including: a first optical layer on the display element; and a second optical layer on the first optical layer; and a thin film encapsulation layer on the optical layer, and including: a first inorganic encapsulation layer on the second optical layer; an auxiliary layer on the first inorganic encapsulation layer; an organic encapsulation layer on the auxiliary layer; and a second inorganic encapsulation layer on the organic encapsulation layer. A refractive index of the second optical layer is smaller than a refractive index of the capping layer, and a refractive index of the first optical layer is between the refractive index of the second optical layer and the refractive index of the capping layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Pat. Application No.17/087,520, filed Nov. 2, 2020, which claims priority to and the benefitof Korean Patent Application No. 10-2020-0038235, filed Mar. 30, 2020,the entire content of both of which is incorporated herein by reference.

BACKGROUND 1. Field

Aspects of embodiments of the present disclosure relate to a displaydevice.

2. Description of the Related Art

In recent years, the purposes of use for display devices have beendiversified. In addition, because the thickness and weight of thedisplay device are being reduced, the range of use of the display deviceis increasing, and thus, research on display devices that may be used invarious fields is continuously being conducted.

Display elements provided in the display device emit light of apredetermined color to provide an image, and the emitted light may passthrough a sealing member for sealing the display elements. In the casewhere the sealing member has a structure in which a plurality of layersare stacked, the light emitted from the display element may undergointerference due to the film thickness of the sealing member.

The above information disclosed in this Background section is forenhancement of understanding of the background of the presentdisclosure, and therefore, it may contain information that does notconstitute prior art.

SUMMARY

One or more example embodiments of the present disclosure are directedto a display device capable of reducing a color shift (e.g., a specificor predetermined color shift) at an angle (e.g., a specific orpredetermined angle) by arranging an optical layer between a displayelement and a sealing member.

However, aspects and features of the present disclosure are not limitedto the above, and the above and other aspects and features of thepresent disclosure will become more apparent to one of ordinary skill inthe art to which the present disclosure pertains by referencing thedetailed description of the present disclosure given below, and/or bypracticing one or more embodiments of the present disclosure.

According to one or more example embodiments of the present disclosure,a display device includes: a substrate; a display element on thesubstrate; a capping layer on the display element; an optical layer onthe capping layer, and including: a first optical layer on the displayelement; and a second optical layer on the first optical layer; and athin film encapsulation layer on the optical layer, and including: afirst inorganic encapsulation layer on the second optical layer; anauxiliary layer on the first inorganic encapsulation layer; an organicencapsulation layer on the auxiliary layer; and a second inorganicencapsulation layer on the organic encapsulation layer. A refractiveindex of the second optical layer is smaller than a refractive index ofthe capping layer, and a refractive index of the first optical layer isbetween the refractive index of the second optical layer and therefractive index of the capping layer.

In an example embodiment, the refractive index of the first opticallayer may be in a range from 1.62 to 1.89, and a thickness of the firstoptical layer may be in a range from 20 nm to 60 nm.

In an example embodiment, the refractive index of the second opticallayer may be in a range from 1.45 to 1.62, and a thickness of the secondoptical layer may be in a range from 40 nm to 100 nm.

In an example embodiment, the refractive index of the capping layer maybe in a range from 1.6 to 2.3, and a thickness of the capping layer maybe in a range from 30 nm to 120 nm.

In an example embodiment, a thickness of the auxiliary layer may be in arange from 30 nm to 100 nm, and a thickness of the first inorganicencapsulation layer may be in a range from 400 nm to 2200 nm.

In an example embodiment, the auxiliary layer may be interposed betweenthe first inorganic encapsulation layer and the organic encapsulationlayer, a refractive index of the first inorganic encapsulation layer maybe greater than a refractive index of the auxiliary layer, and therefractive index of the auxiliary layer may be between the refractiveindex of the first inorganic encapsulation layer and a refractive indexof the organic encapsulation layer.

In an example embodiment, the refractive index of the auxiliary layermay satisfy: min(n1, n2) + |n2 - n1| × 0.25 < n3 < min(n1, n2) + |n2 -n1| × 0.75, where n3 may represent the refractive index of the auxiliarylayer, n1 may represent the refractive index of the first inorganicencapsulation layer, n2 may represent the refractive index of theorganic encapsulation layer, min(n1, n2) may represent a minimum valueof n1 and n2, and |n2 - n1| may represent an absolute value of adifference between n2 and n1.

In an example embodiment, each of the first inorganic encapsulationlayer and the auxiliary layer may include an inorganic insulatingmaterial.

In an example embodiment, the display device may further include: alower layer interposed between the auxiliary layer and the organicencapsulation layer.

In an example embodiment, a refractive index of the auxiliary layer maybe greater than a refractive index of the organic encapsulation layer,and a refractive index of the lower layer may be between the refractiveindex of the auxiliary layer and the refractive index of the organicencapsulation layer.

In an example embodiment, the refractive index of the auxiliary layermay satisfy: min(n1, n2) + |n2 - n1| ×0.25 < n3 < min(n1, n2) + |n2 -n1| ×0.75, where n3 may represent the refractive index of the auxiliarylayer, n1 may represent a refractive index of the first inorganicencapsulation layer, n2 may represent the refractive index of the lowerlayer, min(n1, n2) may represent a minimum value of n1 and n2, and |n2-n1| may represent an absolute value of a difference between n2 and n1.

In an example embodiment, the refractive index of the lower layer may be0.05 less than the refractive index of the organic encapsulation layer,and the lower layer may include an inorganic insulating material.

In an example embodiment, the lower layer and the auxiliary layer mayinclude an inorganic insulating material including a silicon element, anitrogen element, and an oxygen element, and an oxygen content of thelower layer may be greater than an oxygen content of the auxiliarylayer.

In an example embodiment, the first inorganic encapsulation layer mayinclude a plurality of stacked films.

According to one or more example embodiments of the present disclosure,a display device includes: a substrate; organic light emitting diodes onthe substrate; a capping layer on the organic light emitting diodes; anoptical layer on the capping layer, and including: a first optical layeron the organic light emitting diodes; and a second optical layer on thefirst optical layer; and a thin film encapsulation layer on the opticallayer to encapsulate the organic light emitting diodes, and including: afirst inorganic encapsulation layer on the second optical layer; anauxiliary layer on the first inorganic encapsulation layer; an organicencapsulation layer on the auxiliary layer; and a second inorganicencapsulation layer on the organic encapsulation layer. A refractiveindex of the second optical layer is smaller than a refractive index ofthe capping layer, and a refractive index of the first optical layer isbetween the refractive index of the second optical layer and therefractive index of the capping layer.

In an example embodiment, the refractive index of the first opticallayer may be in a range from 1.62 to 1.89, a thickness of the firstoptical layer may be in a range from 20 nm to 60 nm, the refractiveindex of the second optical layer may be in a range from 1.45 to 1.62,and a thickness of the second optical layer may be in a range from 40 nmto 100 nm.

In an example embodiment, the refractive index of the capping layer maybe in a range from 1.6 to 2.3, and a thickness of the capping layer maybe in a range from 30 nm to 120 nm.

In an example embodiment, a thickness of the auxiliary layer may be in arange from 30 nm to 100 nm, and a thickness of the first inorganicencapsulation layer may be in a range from 400 nm to 2200 nm.

In an example embodiment, the auxiliary layer may be interposed betweenthe first inorganic encapsulation layer and the organic encapsulationlayer, a refractive index of the first inorganic encapsulation layer maybe greater than a refractive index of the auxiliary layer, therefractive index of the auxiliary layer may be between the refractiveindex of the first inorganic encapsulation layer and a refractive indexof the organic encapsulation layer, and the refractive index of theauxiliary layer may satisfy: min(n1, n2) + |n2 - n1| ×0.25 < n3 <min(n1, n2) + |n2 - n1| ×0.75, where n3 may represent the refractiveindex of the auxiliary layer, n1 may represent the refractive index ofthe first inorganic encapsulation layer, n2 may represent the refractiveindex of the organic encapsulation layer, min(n1, n2) may represent aminimum value of n1 and n2, and |n2 - n1| may represent an absolutevalue of a difference between n2 and n1.

In an example embodiment, each of the first inorganic encapsulationlayer and the auxiliary layer may include an inorganic insulatingmaterial.

The display device according to one or more example embodiments of thepresent disclosure may reduce a color shift (e.g., a specific orpredetermined color shift) at an angle (e.g., a specific orpredetermined angle) by disposing the optical layer between the displayelement and the sealing member.

However, the aspects and features of the present disclosure are notlimited to the aforementioned aspects and features, and various otheraspects and features are included in the present specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and features of the present disclosure willbecome more apparent to those skilled in the art from the followingdetailed description of the example embodiments with reference to theaccompanying drawings, in which:

FIG. 1 is a plan view schematically showing a display device accordingto an example embodiment;

FIG. 2 illustrates a display element disposed in one pixel region of adisplay device and a pixel circuit connected thereto according to anexample embodiment;

FIG. 3 is a cross-sectional view illustrating a portion of a displaydevice according to an example embodiment;

FIG. 4 is a cross-sectional view illustrating a portion of a displaydevice according to a modified example of the display device of FIG. 3 ;

FIG. 5 is a schematic diagram schematically illustrating a displaydevice according to an example embodiment;

FIG. 6 is a graph illustrating a minimum perceptible color difference(MPCD) when an optical layer according to an example embodiment isomitted;

FIG. 7 is a graph illustrating a minimum perceptible color difference(MPCD) when an optical layer according to an example embodiment isapplied;

FIG. 8 is a cross-sectional view illustrating a portion of a displaydevice according to another embodiment;

FIG. 9 is a schematic diagram schematically illustrating a displaydevice according to another embodiment;

FIG. 10 is a cross-sectional view illustrating a portion of a displaydevice according to a modified example of the display device of FIG. 8 ;

FIG. 11 is a cross-sectional view illustrating a portion of a displaydevice according to still another embodiment; and

FIG. 12 schematically illustrates a display device according to stillanother embodiment.

DETAILED DESCRIPTION

Hereinafter, example embodiments will be described in more detail withreference to the accompanying drawings, in which like reference numbersrefer to like elements throughout. The present disclosure, however, maybe embodied in various different forms, and should not be construed asbeing limited to only the illustrated embodiments herein. Rather, theseembodiments are provided as examples so that this disclosure will bethorough and complete, and will fully convey the aspects and features ofthe present disclosure to those skilled in the art. Accordingly,processes, elements, and techniques that are not necessary to thosehaving ordinary skill in the art for a complete understanding of theaspects and features of the present disclosure may not be described.Further, when an embodiment may be implemented differently, a specificprocess order may be performed differently from the described order. Forexample, two consecutively described processes may be performed at thesame or substantially at the same time or performed in an order oppositeto the described order. Unless otherwise noted, like reference numeralsdenote like elements throughout the attached drawings and the writtendescription, and thus, redundant descriptions thereof may not berepeated.

In the drawings, the relative sizes of elements, layers, and regions maybe exaggerated and/or simplified for clarity. Spatially relative terms,such as “beneath,” “below,” “lower,” “under,” “above,” “upper,” and thelike, may be used herein for ease of explanation to describe one elementor feature’s relationship to another element(s) or feature(s) asillustrated in the figures. It will be understood that the spatiallyrelative terms are intended to encompass different orientations of thedevice in use or in operation, in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” or “under” otherelements or features would then be oriented “above” the other elementsor features. Thus, the example terms “below” and “under” can encompassboth an orientation of above and below. The device may be otherwiseoriented (e.g., rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein should be interpretedaccordingly. Further, in the figures, the x-axis, y-axis, and z-axis arenot limited to three axes on the Cartesian coordinate system, and may beinterpreted in a broad sense including the same. For example, thex-axis, y-axis, and z-axis may be orthogonal to each other, but may alsorefer to different directions that are not orthogonal to each other.

It will be understood that, although the terms “first,” “second,”“third,” etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondescribed below could be termed a second element, component, region,layer or section, without departing from the spirit and scope of thepresent disclosure.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to,” or “coupled to” another element or layer, itcan be directly on, connected to, or coupled to the other element orlayer, or one or more intervening elements or layers may be present.Similarly, when elements, layers, films, regions, or components arereferred to as being “electrically connected” to each other, theelements, the layers, the films, the regions, or the components may bedirectly electrically connected to each other, or may be indirectlyelectrically connected to each other with one or more interveningelements, layers, films, regions, or components being present. Inaddition, it will also be understood that when an element or layer isreferred to as being “between” two elements or layers, it can be theonly element or layer between the two elements or layers, or one or moreintervening elements or layers may also be present.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a” and “an” are intendedto include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes,” and “including,” “has,” “have,”and “having,” when used in this specification, specify the presence ofthe stated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. As used herein, the term “and/or” includes anyand all combinations of one or more of the associated listed items. Forexample, the expression “A and/or B” may include A, B, or A and B.Expressions such as “at least one of,” when preceding a list ofelements, modify the entire list of elements and do not modify theindividual elements of the list.

As used herein, the term “substantially,” “about,” and similar terms areused as terms of approximation and not as terms of degree, and areintended to account for the inherent variations in measured orcalculated values that would be recognized by those of ordinary skill inthe art. Further, the use of “may” when describing embodiments of thepresent disclosure refers to “one or more embodiments of the presentdisclosure.” As used herein, the terms “use,” “using,” and “used” may beconsidered synonymous with the terms “utilize,” “utilizing,” and“utilized,” respectively.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present disclosure belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and/orthe present specification, and should not be interpreted in an idealizedor overly formal sense, unless expressly so defined herein.

FIG. 1 is a plan view schematically showing a display device accordingto an example embodiment.

Referring to FIG. 1 , a display device 10 may include a display area DA,and a non-display area NDA adjacent to the display area DA. For example,in some embodiments, the non-display area NDA may surround (e.g., arounda periphery of) the display area, or may be adjacent to at least one endof the display area DA. The display device 10 includes a plurality ofpixel regions P disposed at (e.g., in or on) the display area DA. Adisplay element capable of emitting light of a desired color (e.g., apredetermined color) may be disposed in each pixel region P, and thedisplay element may be connected to a scan line SL and a data line DL.FIG. 1 may be understood as a state of a substrate 100 of the displaydevice 10. For example, it may be understood that the substrate 100includes the display area DA and the non-display area NDA.

At (e.g., in or on) the non-display area NDA, a scan driver 1100 thatprovides a scan signal to each pixel region P through the scan line SL(e.g., though a corresponding scan line SL), a data driver 1200 thatprovides a data signal to a display element provided in each pixelregion P through the data line DL (e.g., through a corresponding dataline DL), and main power wiring for providing first and second powersupply voltages may be disposed.

FIG. 1 illustrates that the data driver 1200 is disposed on thesubstrate 100, but in another embodiment, the data driver 1200 may bedisposed on a flexible printed circuit board (FPCB) that is electricallyconnected to a pad disposed on one side of the display device 10.

The display device 10 according to an embodiment of the presentdisclosure may include an organic light emitting display, an inorganiclight emitting display, a quantum dot display, or the like. Hereinafter,for convenience, an organic light emitting display may be described asthe display device according to an embodiment of the present disclosure,but the present disclosure is not limited thereto, and the aspects andfeatures of one or more example embodiments of the present disclosuredescribed in more detail below may be applied to various suitable kindsof display devices, such as at least the different kinds of displaydevices described above.

FIG. 2 illustrates a display element disposed in one pixel region of adisplay device and a pixel circuit connected thereto according to anexample embodiment.

Referring to FIG. 2 , an organic light emitting diode OLED, which is adisplay element, is connected to a pixel circuit PC. The pixel circuitPC may include a first thin film transistor T1, a second thin filmtransistor T2, and a storage capacitor Cst. The organic light emittingdiode OLED may emit, for example, red, green, or blue light, or asanother example, may emit red, green, blue, or white light.

The second thin film transistor T2 is a switching thin film transistor,and is connected to the scan line SL and the data line DL. The secondthin film transistor T2 may transfer a data voltage (e.g., the datasignal), which is input from the data line DL, to the first thin filmtransistor T1 according to a switching voltage (e.g., the scan signal)input from the scan line SL. The storage capacitor Cst may be connectedto (e.g., may be connected between) the second thin film transistor T2and a driving voltage line PL. The storage capacitor Cst may store avoltage corresponding to a difference between a voltage received fromthe second thin film transistor T2 and a first power supply voltageELVDD supplied to the driving voltage line PL.

The first thin film transistor T1 may be, as a driving thin filmtransistor, connected to the driving voltage line PL and the storagecapacitor Cst, and may control a driving current flowing through theorganic light emitting diode OLED from the driving voltage line PL inresponse to the voltage (e.g., a voltage value) stored in the storagecapacitor Cst. The organic light emitting diode OLED may emit lighthaving a desired luminance (e.g., a predetermined luminance) accordingto the driving current. A counter electrode (e.g., a cathode) of theorganic light emitting diode OLED may be supplied with a second powersupply voltage ELVSS.

FIG. 2 illustrates that the pixel circuit PC includes two thin filmtransistors and one storage capacitor, but the present disclosure is notlimited thereto, and in other embodiments, the number of thin filmtransistors and/or the number of storage capacitors may be variouslymodified depending on a structure or a design of the pixel circuit PC.

FIG. 3 is a cross-sectional view illustrating a portion of a displaydevice according to an example embodiment.

Referring to FIG. 3 , a pixel circuit layer PCL including a pixelcircuit is disposed on the substrate 100. The organic light emittingdiode OLED, which may be a display element, is disposed on the pixelcircuit layer PCL, and the organic light emitting diode OLED may becovered by a thin film encapsulation layer 300.

The substrate 100 may include a polymer resin. The substrate 100including the polymer resin may have flexible, rollable, and/or bendablecharacteristics.

In an embodiment, the substrate 100 may include a first base layer 101,a first barrier layer 102, a second base layer 103, and a second barrierlayer 104 as shown in FIG. 3 . Each of the first base layer 101 and thesecond base layer 103 may include a polymer resin. For example, thefirst base layer 101 and the second base layer 103 may include a polymerresin such as polyethersulfone (PES), polyarylate (PAR), polyetherimide(PEI), polyethylene naphthalate (PEN), polyethylene terephthalate (PET),polyphenylene sulfide (PPS), polyimide (PI), polycarbonate (PC),cellulose triacetate (TAC), and/or cellulose acetate propionate (CAP).The first barrier layer 102 and the second barrier layer 104 may bebarrier layers that prevent or substantially prevent the penetration offoreign substances, and may each be a single layer structure or amultilayered structure including one or more inorganic materials, forexample, such as silicon nitride and/or silicon oxide.

FIG. 4 is a cross-sectional view illustrating a portion of a displaydevice according to a modified example of the display device of FIG. 3 .

As a modified example, the substrate 100 may be a single layer structureincluding a glass material as illustrated in FIG. 4 , instead of themultilayered structure as illustrated in FIG. 3 . For example, thesubstrate 100 may be a glass substrate with SiO2 as a main component.

Referring to FIGS. 3 and 4 , in some embodiments, the pixel circuitlayer PCL on the substrate 100 of FIGS. 3 and 4 may include a thin filmtransistor TFT, and a storage capacitor (e.g., Cst in FIG. 2 ) connectedto the thin film transistor TFT. The structure of the thin filmtransistor TFT may have the same or substantially the same structure foreach pixel. The thin film transistor TFT of each pixel may be connectedto a display element provided in each pixel.

The thin film transistor TFT may include a semiconductor layer ACT, agate electrode GE, a source electrode SE, and a drain electrode DE. Thesemiconductor layer ACT may include amorphous silicon, polycrystallinesilicon, or an organic semiconductor material. In order to secure theinsulating property between the semiconductor layer ACT and the gateelectrode GE, a gate insulating layer 121 including an inorganicmaterial, for example, such as silicon oxide, silicon nitride, and/orsilicon oxynitride, may be interposed between the semiconductor layerACT and the gate electrode GE. An interlayer insulating layer 131including an inorganic material, for example, such as silicon oxide,silicon nitride, and/or silicon oxynitride, may be disposed on the gateelectrode GE, and the source electrode SE and the drain electrode DE maybe disposed on the interlayer insulating layer 131. The insulating layer(e.g., the gate insulating layer 121, the interlayer insulating layer131, and/or the like) containing the inorganic material may be formedthrough chemical vapor deposition (CVD) or atomic layer deposition(ALD).

The gate electrode GE, the source electrode SE, and the drain electrodeDE may be formed of various suitable conductive materials. The gateelectrode GE may include, for example, molybdenum or aluminum, and mayhave a single layer structure or a multilayered structure. For example,the gate electrode GE may be a single layer of molybdenum, or may have athree-layered structure including a molybdenum layer, an aluminum layer,and a molybdenum layer. The source electrode SE and the drain electrodeDE may include titanium or aluminum, and may have a single layerstructure or a multilayered structure. In an embodiment, the sourceelectrode SE and the drain electrode DE may have a three-layeredstructure including a titanium layer, an aluminum layer, and a titaniumlayer.

A buffer layer 110 including an inorganic material, for example, such assilicon oxide, silicon nitride, and/or silicon oxynitride, may beinterposed between the thin film transistor TFT and the substrate 100(e.g., having the above-described structure of FIG. 3 or FIG. 4 ). Thebuffer layer 110 may serve to enhance the smoothness of the uppersurface of the substrate 100, and/or to prevent or to substantiallyprevent (e.g., to minimize) impurities from penetrating from thesubstrate 100 or the like into the semiconductor layer ACT of the thinfilm transistor TFT.

A planarization insulating layer 140 may be disposed on the thin filmtransistor TFT. The planarization insulating layer 140 may be formed ofan organic material, for example, such as acryl, benzocyclobutene (BCB),or hexamethyldisiloxane (HMDSO). In FIGS. 3 and 4 , the planarizationinsulating layer 140 is illustrated as a single layer structure, but maybe a multilayered structure.

The organic light emitting diode OLED includes a pixel electrode 221, anintermediate layer 222, and a counter electrode 223.

The pixel electrode 221 is disposed on the planarization insulatinglayer 140, and may be disposed one for each pixel. The pixel electrode221 may be a reflective electrode. In an embodiment, the pixel electrode221 may include a reflective film containing, for example, silver (Ag),magnesium (Mg), aluminum (Al), platinum (Pt), palladium (Pd), gold (Au),nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), or a compoundthereof. In another embodiment, the pixel electrode 221 may include atransparent or translucent electrode layer disposed above and/or belowthe reflective film described above. The above-described transparent ortranslucent electrode layer may include, for example, at least oneselected from the group consisting of indium tin oxide (ITO), indiumzinc oxide (IZO), zinc oxide (ZnO), indium oxide (in₂O₃), indium galliumoxide (IGO), and aluminum zinc oxide (AZO). In some embodiments, thepixel electrode 221 may have a three-layered structure of an ITO layer,an Ag layer, and an ITO layer.

A pixel defining film 150 is disposed on the pixel electrodes 221. Thepixel defining film 150 has an opening 1500P exposing the centralportion of each pixel electrode 221. The pixel defining film 150 mayincrease the distance between the edge of the pixel electrode 221 andthe counter electrode 223, thereby preventing or substantiallypreventing an arc or the like from occurring at the edge of the pixelelectrode 221. The pixel defining film 150 may include an organicinsulating material, for example, such as polyimide, polyamide, acrylicresin, benzocyclobutene, hexamethyldisiloxane (HMDSO), and/or phenolresin, and may be formed by a method such as spin coating.

In some embodiments, the intermediate layer 222 may include a firstfunctional layer 222 a, a light emitting layer 222 b, and a secondfunctional layer 222 c. The light emitting layer 222 b may be disposedon the pixel electrode 221 exposed through the opening 1500P of thepixel defining film 150. The light emitting layer 222 b may include anorganic material including, for example, a fluorescent or phosphorescentmaterial capable of emitting red, green, or red light. The organicmaterial of the light emitting layer 222 b may be a low molecularorganic material or a high molecular organic material.

The first functional layer 222 a and the second functional layer 222 cmay be disposed below and above the light emitting layer 222 b,respectively. The first functional layer 222 a may include, for example,a hole transport layer (HTL), or a hole transport layer and a holeinjection layer (HIL). The second functional layer 222 c may be anelement disposed on the light emitting layer 222 b, and may include, forexample, an electron transport layer (ETL) and/or an electron injectionlayer (EIL). However, the present disclosure is not limited thereto, andthe second functional layer 222 c may be optional. For example, in someembodiments, the second functional layer 222 c may not be provided(e.g., may be omitted).

While the light emitting layers 222 b are respectively disposed tocorrespond to the openings 1500P of the pixel defining film 150, thefirst functional layer 222 a and the second functional layer 222 c maybe a common layer that are integrally formed to cover the substrate 100as a whole (e.g., to cover an entirety of at least the display area DA),similar to the counter electrode 223 described in more detail below, forexample, to cover the entire display area DA of the substrate 100.

In some embodiments, the counter electrode 223 may include a (semi)transparent layer containing, for example, silver (Ag), magnesium (Mg),aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni),neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca),an alloy thereof, or the like. In another embodiment, the counterelectrode 223 may further include a layer such as ITO, IZO, ZnO, orIn203 on the (semi) transparent layer containing the one or more of theaforementioned materials. In an embodiment, the counter electrode 223may include silver (Ag), magnesium (Mg), or an alloy of silver (Ag) andmagnesium (Mg).

A capping layer 230 may be disposed on the counter electrode 223. Forexample, the capping layer 230 may include LiF, an inorganic insulatingmaterial, or an organic insulating material. The capping layer 230 maycover and protect the counter electrode 223 from the top (e.g., a topsurface) of the counter electrode 223.

An optical layer 240 may be disposed on the capping layer 230. Theoptical layer 240 may include two or more stacked layers. For example,the optical layer 240 may include a first optical layer 241, and asecond optical layer 245 disposed on the first optical layer 241. Thefirst optical layer 241 may be disposed on the capping layer 230. Thefirst optical layer 241 may be interposed between the capping layer 230and the second optical layer 245. The term ‘interposed’ as used hereinrefers to a corresponding component that is in direct contact with upperand lower components between which the corresponding component isinterposed. In other words, the first optical layer 241 may directlycontact the capping layer 230 and the second optical layer 245.

The optical layer 240 may include an inorganic insulating material. Forexample, the optical layer 240 may include one or more inorganicinsulating materials selected from the group consisting of aluminumoxide, titanium oxide, tantalum oxide, hafnium oxide, zinc oxide,silicon oxide, silicon nitride, and silicon oxynitride. The materials ofthe first optical layer 241 and the second optical layer 245 may bedifferent from each other, or may be the same as each other.

As described above, the display elements provided in the display deviceemit light of a desired color (e.g., a predetermined color) to providean image, and the emitted light may pass through the thin filmencapsulation layer 300 (which will be described in more detail below)for sealing the display elements. When the thin film encapsulation layer300 has a structure in which a plurality of layers are stacked, as in anembodiment described in more detail below, light emitted from thedisplay element may undergo interference due to the film thickness ofthe thin film encapsulation layer 300. Due to the generatedinterference, a user may observe the screen of the display device to begreenish (e.g., to turn greenish) at a large viewing angle (e.g., 60° ormore). However, according to the display device of one or more exampleembodiments of the present disclosure, as described in more detailbelow, by adjusting the refractive index and the thickness of theoptical layer 240, a phenomenon in which the user may observe the screenof the display device to be greenish at a large viewing angle (e.g., 60°or more) due to the generated interference may be prevented orsubstantially prevented.

The thin film encapsulation layer 300 may be disposed on the opticallayer 240. The thin film encapsulation layer 300 may include at leastone inorganic encapsulation layer and at least one organic encapsulationlayer. For example, as illustrated in FIGS. 3 and 4 , the thin filmencapsulation layer 300 may include a first inorganic encapsulationlayer 310 on the second optical layer 245, an organic encapsulationlayer 320 on the first inorganic encapsulation layer 310, and a secondinorganic encapsulation layer 330 on the organic encapsulation layer320. The thin film encapsulation layer 300 may include an auxiliarylayer 315 interposed between the first inorganic encapsulation layer 310and the organic encapsulation layer 320.

In some embodiments, the first inorganic encapsulation layer 310 and thesecond inorganic encapsulation layer 330 may include one or moreinorganic insulating materials selected from the group consisting ofaluminum oxide, titanium oxide, tantalum oxide, hafnium oxide, zincoxide, silicon oxide, silicon nitride, and silicon oxynitride. In someembodiments, the first inorganic encapsulation layer 310 and the secondinorganic encapsulation layer 330 may include an inorganic insulatinglayer including a non-metallic element, for example, such as siliconoxide, silicon nitride, or silicon oxynitride. The number and/or type ofnon-metallic elements included in the first inorganic encapsulationlayer 310 may be different from the number and/or type of non-metallicelements included in the second inorganic encapsulation layer 330. Forexample, the first inorganic encapsulation layer 310 may include siliconoxynitride, and the second inorganic encapsulation layer 330 may includesilicon nitride, but the present disclosure is not limited thereto.

The organic encapsulation layer 320 may relieve internal stress of thefirst inorganic encapsulation layer 310 and/or the second inorganicencapsulation layer 330. The organic encapsulation layer 320 may includea polymer-based material. Polymer-based materials may include, forexample, polyethylene terephthalate, polyethylene naphthalate,polycarbonate, polyimide, polyethylene sulfonate, polyoxymethylene,polyarylate, hexamethyldisiloxane, acrylic resins (e.g., polymethylmethacrylate, polyacrylic acid, or the like), or any suitablecombination thereof.

In some embodiments, the organic encapsulation layer 320 may be formedby applying a monomer layer having a flow property, and curing themonomer layer using heat or light, for example, such as ultravioletlight. In another embodiment, the organic encapsulation layer 320 may beformed by applying one or more of the above-described polymer-basedmaterials.

The auxiliary layer 315 is interposed between the first inorganicencapsulation layer 310 and the organic encapsulation layer 320. Theauxiliary layer 315 may directly contact the first inorganicencapsulation layer 310 and the organic encapsulation layer 320. Forexample, the bottom surface of the auxiliary layer 315 may directlycontact the top surface of the first inorganic encapsulation layer 310,and the top surface of the auxiliary layer 315 may directly contact thebottom surface of the organic encapsulation layer 320.

The auxiliary layer 315 may be an inorganic insulating layer containinga non-metal element. In an embodiment, the non-metal element containedin the auxiliary layer 315 may be the same non-metal element as that ofthe first inorganic encapsulation layer 310, and the non-metal elementmay be, for example, silicon (Si), oxygen (O), and/or nitrogen (N).

The light emitted from the organic light emitting diode OLED disposed ineach pixel passes through the thin film encapsulation layer 300 to theoutside. At this time, due to the thin film interference phenomenon ofthe thin film encapsulation layer 300 discussed above, the user mayobserve an image that may be greenish as a whole when viewed in adirection (e.g., a z direction) perpendicular to and a direction obliqueto the substrate 100. According to the display device of one or moreexample embodiments of the present disclosure, however, as describedabove, by adjusting the refractive index and the thickness of theoptical layer 240, the phenomenon in which the user may observe thescreen of the display device to be greenish at a large viewing angle(e.g., 60° or more) due to the generated interference may be preventedor substantially prevented.

FIG. 5 is a schematic diagram schematically illustrating a displaydevice according to an example embodiment.

Referring to FIG. 5 , the display device 10 includes the substrate 100,the pixel circuit layer PCL, a display layer 200, and the thin filmencapsulation layer 300, which are sequentially stacked on one another.The display layer 200 may include the pixel electrode 221, theintermediate layer 222, the counter electrode 223, the capping layer230, and the optical layer 240, which are sequentially stacked on oneanother.

The optical layer 240 may include the first optical layer 241 and thesecond optical layer 245 sequentially arranged along a light travelingdirection (e.g., a direction from the display layer 200 toward the thinfilm encapsulation layer 300).

The thin film encapsulation layer 300 may include the first inorganicencapsulation layer 310 and the auxiliary layer 315 sequentiallydisposed along the light traveling direction (e.g., the direction fromthe display layer 200 toward the thin film encapsulation layer 300). Theorganic encapsulation layer 320 and the second inorganic encapsulationlayer 330 may be disposed on the auxiliary layer 315.

The capping layer 230 may have a first thickness t1. The first thicknesst1 may be in a range from about 30 nm to about 120 nm. The refractiveindex of the capping layer 230 may be in a range from about 1.6 to 2.3.For example, the first thickness t1 of the capping layer 230 may beabout 64 nm, and the refractive index of the capping layer 230 may beabout 1.97, but the present disclosure is not limited thereto.

The first optical layer 241 may have a second thickness t2. The secondthickness t2 may be in a range from about 20 nm to about 60 nm. Therefractive index of the first optical layer 241 may be in a range fromabout 1.62 to 1.89. For example, the second thickness t2 of the firstoptical layer 241 may be about 40 nm, and the refractive index of thefirst optical layer 241 may be about 1.77, but the present disclosure isnot limited thereto.

The second optical layer 245 may have a third thickness t3. The thirdthickness t3 may be in a range from about 40 nm to about 100 nm. Therefractive index of the second optical layer 245 may be in a range fromabout 1.45 to 1.62. For example, the third thickness t3 of the secondoptical layer 245 may be about 60 nm, and the refractive index of thesecond optical layer 245 may be about 1.52, but the present disclosureis not limited thereto.

Accordingly, in some embodiments, the refractive index of the firstoptical layer 241 may be between the refractive indices of the secondoptical layer 245 and the capping layer 230, for example, such that therefractive index of the first optical layer 241 may be greater than therefractive index of the second optical layer 245 and less than therefractive index of the capping layer 230. According to the presentembodiment, by disposing the first optical layer 241, which may have arefractive index having a value between the refractive index of thesecond optical layer 245 and the refractive index of the capping layer230, between the capping layer 230 and the second optical layer 245, thecapping layer 230 and the first optical layer 241 having higherrefractive indices compared to that of the second optical layer 245, itmay be possible to prevent or substantially prevent the screen of thedisplay device from being observed as being greenish at a large viewingangle (e.g., θ = 60° or more) in the color coordinates of the displaydevice 10.

Further, the capping layer 230 may have a thickness in the range of thefirst thickness t1, thereby improving a distribution of the thickness ofthe intermediate layer 222 of the organic light emitting diode OLED. Inother words, by allowing the capping layer 230 to have the firstthickness t1 of 30 nm or more, the thickness distribution of theintermediate layer 222 of the organic light emitting diode OLEDdescribed above may be improved, and by allowing the capping layer 230to have the first thickness t1 of 120 nm or less, it may be possible toprevent or substantially prevent the capping layer 230 from being peeledoff or separated.

By allowing the first optical layer 241 to have the second thickness t2of 20 nm or more, it may be possible to prevent or substantially preventthe screen of the display device from being greenish at a large viewingangle (e.g., θ = 60° or more) in the color coordinates of the displaydevice 10, and by allowing the first optical layer 241 to have thesecond thickness t2 of 60 nm or less, it may be possible to prevent orsubstantially prevent the first optical layer 241 from being peeled offor separated. Similarly, by allowing the second optical layer 245 tohave the third thickness t3 of 40 nm or more, it may be possible toprevent or substantially prevent the screen of the display device frombeing observed as being greenish at a large viewing angle (e.g., θ = 60°or more) in the color coordinates of the display device 10, and byallowing the second optical layer 245 to have the third thickness t3 of100 nm or less, it may be possible to prevent or substantially preventthe second optical layer 245 from being peeled off or separated.

The first inorganic encapsulation layer 310 may be disposed on thesecond optical layer 245.

The first inorganic encapsulation layer 310 may have a fourth thicknesst4 in a range from about 600 nm to 2200 nm. When the fourth thickness t4of the first inorganic encapsulation layer 310 is 600 nm or more,moisture permeation may be prevented or substantially prevented, andwhen the fourth thickness t4 of the first inorganic encapsulation layer310 is 2200 nm or less, it may be possible to prevent or substantiallyprevent the first inorganic encapsulation layer 310 from being peeledoff or separated. The thickness of the second inorganic encapsulationlayer 330 may be the same or substantially the same as that of the firstinorganic encapsulation layer 310, or may be different (e.g., may besmaller or larger) than that of the first inorganic encapsulation layer310.

On the other hand, light emitted from the display element passes throughthe thin film encapsulation layer 300 such that interference of light orthe like may occur, and although the interference of light may becontrolled (e.g., may be designed) by using the above-described opticallayer 240 to prevent or substantially prevent the screen of the displaydevice from appearing greenish at a large viewing angle (e.g., θ = 60°or more) in the color coordinates of the display device 10, a largevariation in the color coordinates may occur. In order to reduce thelarge variation in the color coordinates, a method of adjusting thethickness of the first inorganic encapsulation layer 310 may beconsidered, but controlling the thickness may not be practically easydue to the error of an equipment itself (e.g., a CVD equipment) used forforming the first inorganic encapsulation layer 310. For example, thefirst inorganic encapsulation layer 310, which protects or substantiallyprotects the display layer 200 from moisture and/or the like, may have athickness in a range of about 600 nm to 2200 nm as described above, toprevent or substantially prevent separation of the first inorganicencapsulation layer 310 or the like. For example, when the error of theequipment used for forming the first inorganic insulating encapsulationlayer 310 is about 10%, a deviation in the thickness of the firstinorganic encapsulation layer 310 that is actually formed may correspondto a range of tens to hundreds of nanometers. Thus, it may bepractically difficult to control the thickness of the first inorganicencapsulation layer 310 to reduce a variation in the minimal perceptiblecolor difference (MPCD), and there may be a limitation in reducing thevariation in the MPCD.

Accordingly, the thin film encapsulation layer 300 according to anexample embodiment may include the auxiliary layer 315 on the firstinorganic encapsulation layer 310, thereby reducing a variation in theMPCD described above, regardless of the thickness of the first inorganicencapsulation layer 310.

The auxiliary layer 315 may be formed of an inorganic insulatingmaterial, and may have a fifth thickness t5 suitable for reducing (e.g.,minimizing) or preventing a variation in the MPCD described above. Forexample, the fifth thickness t5 may be 100 nm or less. In someembodiments, for example, the fifth thickness t5 of the auxiliary layer315 may be in a range of about 30 nm to 100 nm. When the fifth thicknesst5 of the auxiliary layer 315 is 100 nm or less, control of the fifththickness t5 of the auxiliary layer 315 may be performed (e.g., may beeasily performed).

The auxiliary layer 315 may include an inorganic insulating material. Asdescribed above, an inorganic insulating material layer formed by usingthe CVD equipment may have an error of about 10% corresponding to thethickness that may be actually formed when compared to a targetthickness. Because the auxiliary layer 315 may be formed using the CVDequipment in a similar manner (e.g., in the same or substantially thesame way) as that of the first inorganic encapsulation layer 310, thethickness of the auxiliary layer 315 that is actually formed may bedifferent from the target thickness. However, because the thickness ofthe auxiliary layer 315 may be more than tens of times smaller than thethickness of the first inorganic encapsulation layer 310, it may beeasier (e.g., in may be much easier) to control the thickness of theauxiliary layer 315 regardless of the error (e.g., an error of about10%) of the thickness according to the CVD equipment used.

The first inorganic encapsulation layer 310 and the auxiliary layer 315may have different refractive indices from each other. For example, therefractive index n3 of the auxiliary layer 315 may satisfy the followingcondition:

min (n1, n2) + |n2 - n1| × 0.25 < n3 < min (n1, n2) + |n2 - n1| × 0.75

Here, n1 represents the refractive index of the first inorganicencapsulation layer, n2 represents the refractive index of the organicencapsulation layer, min(n1, n2) represents the minimum value of n1 andn2, and |n2 - n1| represents the absolute value of the differencebetween n2 and n1.

When the refractive index n3 of the auxiliary layer 315 is within theabove-described range, it may be possible to reduce (e.g., to minimize)or to prevent the occurrence of a large variation of the MPCD.

FIG. 6 is a graph illustrating a minimum perceptible color difference(MPCD) when the optical layer according to an example embodiment isomitted. FIG. 7 is a graph illustrating a minimum perceptible colordifference (MPCD) when the optical layer according to an exampleembodiment is applied. FIG. 6 shows the MPCD when the above-describedoptical layer 240 is omitted, and FIG. 7 shows the MPCD when theabove-described optical layer 240 is included (e.g., is disposed).

Referring to FIGS. 6 and 7 , the MPCD is illustrated as a contour lineby dividing a section (e.g., a predetermined section), and the MPCDillustrates that having a negative (-) value in a direction away from 0(zero) with respect to the vertical axis indicates a color appearinggreenish, and having a positive (+) value in a direction away from 0(zero) with respect to the vertical axis indicates a color appearingbluish.

The contour line of the MPCD is illustrated based on the MPCD value whenthe display device 10 is viewed in a direction perpendicular to and adirection oblique to the substrate 100, for example, at 0° (e.g., in thez direction) and at an oblique angle of about 30°, 45°, and 60° withrespect to the z direction, as illustrated in FIG. 5 .

According to the example of FIG. 6 , it is shown that the screen of thedisplay device may appear greenish at a large viewing angle (e.g., θ =60° or more) in the MPCD of the corresponding display device. On theother hand, according to the embodiment of FIG. 7 , by disposing thefirst optical layer 241, which may have a refractive index having avalue between the refractive index of the second optical layer 245 andthe refractive index of the capping layer 230, between the capping layer230 and the second optical layer 245, the capping layer 230 and thefirst optical layer 241 having higher refractive indices compared tothat of the second optical layer 245, it may be possible to reduce(e.g., to minimize) or to prevent a phenomenon in that the screen of thedisplay device appears greenish at a large viewing angle (e.g., θ = 60°or more) in the MPCD of the display device 10.

Hereinafter, a display device according to another embodiment will bedescribed with reference to FIGS. 8 and 9 . In the embodiment of FIGS. 8and 9 , the same or substantially the same components as those of one ormore of the above-described embodiments are denoted by the samereference numerals, and thus, redundant description thereof may besimplified or may not be repeated.

FIG. 8 is a cross-sectional view illustrating a portion of a displaydevice according to another embodiment. FIG. 9 is a schematic diagramschematically illustrating a display device according to anotherembodiment.

Referring to FIGS. 8 and 9 , the display device may include thesubstrate 100, the pixel circuit layer PCL, the display layer 200, and athin film encapsulation layer 300_1, which are sequentially stacked onone another. The thin film encapsulation layer 300_1 may be similar tothe thin film encapsulation layer 300 described above, except the thinfilm encapsulation layer 300_1 may further include a lower layer 317disposed under the organic encapsulation layer 320. Except for the lowerlayer 317, the other elements shown in FIGS. 8 and 9 are the same orsubstantially the same as those of the embodiment described withreference to FIGS. 3 and 5 , such that the following description may befocused on the lower layer 317.

The lower layer 317 may be interposed between the organic encapsulationlayer 320 and the auxiliary layer 315.

The lower layer 317 may not have a role as a thin film encapsulationlayer, for example, such as reducing moisture permeability. The lowerlayer 317 may control a material for forming the organic encapsulationlayer 320 during the process for forming the organic encapsulation layer320, for example, when applying and curing the monomer.

The lower layer 317 may be a layer having no separate optical functionas well as having no moisture permeability reducing function asdescribed above, and the refractive index of the lower layer 317 may bethe same or substantially the same as the refractive index of theorganic encapsulation layer 320. The refractive index of the lower layer317 and the refractive index of the organic encapsulation layer 320 maybe the same or substantially the same as each other when a difference Δnbetween the refractive index of the lower layer 317 and the refractiveindex of the organic encapsulation layer 320 is less than 0.05. Forexample, in an embodiment, the refractive index of the lower layer 317may be 1.52.

The thickness of the lower layer 317 may be selected in the range ofabout 50 nm to 100 nm, for example, such as about 55 nm to 90 nm, or 60nm to 85 nm. Although the refractive index of the lower layer 317 andthe refractive index of the organic encapsulation layer 320 may be thesame or substantially the same as each other, an interface may existbetween the lower layer 317 and the organic encapsulation layer 320,which may be in contact with each other, because the lower layer 317 andthe organic encapsulation layer 320 may include different materials fromeach other.

The lower layer 317 may include an inorganic insulating layer. Forexample, the lower layer 317 may contain a non-metallic element like thefirst inorganic encapsulation layer 310 and the auxiliary layer 315, ormay contain an element and/or material different from the non-metallicelement included in the first inorganic encapsulation layer 310 and theauxiliary layer 315. For example, the lower layer 317 may be aninorganic insulating layer having a relatively high oxygen content, forexample, such as an O-rich silicon oxynitride layer.

For example, the first inorganic encapsulation layer 310, the auxiliarylayer 315, and the lower layer 317 may each include the same non-metalelement as each other, such as silicon (Si), oxygen (O), and/or nitrogen(N). A first silicon oxynitride layer as the first inorganicencapsulation layer 310, a second silicon oxynitride layer as theauxiliary layer 315, and a third silicon oxynitride layer as the lowerlayer 317 may have different content ratios of silicon (Si), oxygen (O),and nitrogen (N), respectively. Accordingly, an interface may existbetween the first silicon oxynitride layer and the second siliconoxynitride layer, and an interface may exist between the second siliconoxynitride layer and the third silicon oxynitride layer.

For example, the refractive index n3 of the auxiliary layer 315 maysatisfy the following condition:

min (n1, n2) + |n2 - n1| × 0.25 < n3 < min (n1, n2) + |n2 - n1| × 0.75

Here, n1 represents the refractive index of the first inorganicencapsulation layer, n2 represents the refractive index of the organicencapsulation layer, min(n1, n2) represents the minimum value of n1 andn2, and |n2 - n1| represents the absolute value of the differencebetween n2 and n1.

In the present embodiment, by disposing a first optical layer 241, whichmay have a refractive index having a value between the refractive indexof a second optical layer 245 and the refractive index of the cappinglayer 230, between the capping layer 230 and the second optical layer245, the capping layer 230 and the first optical layer 241 having higherrefractive indices compared to that of the second optical layer 245, itmay be possible to reduce (e.g., to minimize) or to prevent a phenomenonin that the screen of the display device appears greenish at a largeviewing angle (e.g., θ = 60° or more) in the MPCD of the display device10.

FIG. 10 is a cross-sectional view illustrating a portion of a displaydevice according to a modified example of the display device of FIG. 8 .

Referring to FIG. 10 , as a modified example of the display device ofFIG. 8 , the substrate 100 may have a single layer structure including aglass material. For example, the substrate 100 may be a glass substrateincluding SiO2 as a main component.

In the present embodiment, by disposing a first optical layer 241, whichmay have a refractive index having a value between the refractive indexof a second optical layer 245 and the refractive index of the cappinglayer 230, between the capping layer 230 and the second optical layer245, the capping layer 230 and the first optical layer 241 having higherrefractive indices compared to that of the second optical layer 245, itmay be possible to reduce (e.g., to minimize) or to prevent a phenomenonin that the screen of the display device appears greenish at a largeviewing angle (e.g., θ = 60° or more) in the MPCD of the display device10.

FIG. 11 is a cross-sectional view illustrating a portion of a displaydevice according to still another embodiment. FIG. 12 schematicallyillustrates a display device according to still another embodiment.

Referring to FIGS. 11 and 12 , the display device according to thepresent embodiment may be different from the display device of FIGS. 4and 5 in that a thin film encapsulation layer 300_2 may include a firstinorganic encapsulation layer 310_1 having a multilayered structure,which may be different from the first inorganic encapsulation layer 310of FIGS. 4 and 5 . Except for the first inorganic encapsulation layer310_1, the other elements shown in FIGS. 11 and 12 may be the same orsubstantially the same as those of the embodiments described withreference to FIGS. 4 and 5 , such that the following description may befocused on the first inorganic encapsulation layer 310_1.

In more detail, in the display device 10 according to the presentembodiment, the thin film encapsulation layer 300_2 may include thefirst inorganic encapsulation layer 310_1.

The first inorganic encapsulation layer 310_1 may include a plurality ofstacked layers. For example, the first inorganic encapsulation layer310_1 may include a first sub inorganic encapsulation layer 310 ainterposed between the second optical layer 245 and a second subinorganic encapsulation layer 310 b, and the second sub inorganicencapsulation layer 310 b interposed between the first sub inorganicencapsulation layer 310 a and the auxiliary layer 315. Although it isillustrated in FIGS. 11 and 12 that the first inorganic encapsulationlayer 310_1 includes two stacked films that are sequentially stacked,the present disclosure is not limited thereto, and the first inorganicencapsulation layer 310_1 may include three or more stacked films thatare sequentially stacked.

A sum of the thicknesses of the first sub inorganic encapsulation layer310 a and the second sub inorganic encapsulation layer 310 b may have arange that is the same or substantially the same as that of the fourththickness t4 (e.g., from about 600 nm to 2200 nm) of the first inorganicencapsulation layer 310 described with reference to FIGS. 4 and 5 . Thethickness of the first sub inorganic encapsulation layer 310 a may bedifferent from or the same as the thickness of the second sub inorganicencapsulation layer 310 b.

The refractive indices of each of the first sub inorganic encapsulationlayer 310 a and the second sub inorganic encapsulation layer 310 b maybe selected to be within the refractive index range of the firstinorganic encapsulation layer 310 described above with reference to FIG.5 . For example, the refractive indices of the first sub inorganicencapsulation layer 310 a and the second sub inorganic encapsulationlayer 310 b may be the same or substantially the same as each other.

In the present embodiment, by disposing a first optical layer 241, whichmay have a refractive index having a value between the refractive indexof a second optical layer 245 and the refractive index of the cappinglayer 230, between the capping layer 230 and the second optical layer245, the capping layer 230 and the first optical layer 241 having higherrefractive indices compared to that of the second optical layer 245, itmay be possible to reduce (e.g., to minimize) or to prevent a phenomenonin that the screen of the display device appears greenish at a largeviewing angle (e.g., θ = 60° or more) in the MPCD of the display device10.

Although some example embodiments have been described, those skilled inthe art will readily appreciate that various modifications are possiblein the example embodiments without departing from the spirit and scopeof the present disclosure. It will be understood that descriptions offeatures or aspects within each embodiment should typically beconsidered as available for other similar features or aspects in otherembodiments, unless otherwise described. Thus, as would be apparent toone of ordinary skill in the art, features, characteristics, and/orelements described in connection with a particular embodiment may beused singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwisespecifically indicated. Therefore, it is to be understood that theforegoing is illustrative of various example embodiments and is not tobe construed as limited to the specific example embodiments disclosedherein, and that various modifications to the disclosed exampleembodiments, as well as other example embodiments, are intended to beincluded within the spirit and scope of the present disclosure asdefined in the appended claims, and their equivalents.

What is claimed is:
 1. A display device comprising: a substrate; adisplay element on the substrate; a capping layer on the displayelement; a first inorganic layer on the capping layer; a secondinorganic layer on the first inorganic layer; a third inorganic layer onthe second inorganic layer; a fourth inorganic layer on the thirdinorganic layer; an organic layer on the fourth inorganic layer; and afifth inorganic layer on the organic layer, wherein a refractive indexof the second inorganic layer is different from a refractive index ofthe capping layer, and wherein a refractive index of the first inorganiclayer is between the refractive index of the second inorganic layer andthe refractive index of the capping layer.
 2. The display device ofclaim 1, wherein the refractive index of the first inorganic layer is ina range from 1.62 to 1.89, and a thickness of the first inorganic layeris in a range from 20 nm to 60 nm.
 3. The display device of claim 2,wherein the refractive index of the second inorganic layer is in a rangefrom 1.45 to 1.62, and a thickness of the second inorganic layer is in arange from 40 nm to 100 nm.
 4. The display device of claim 1, whereinthe refractive index of the capping layer is in a range from 1.6 to 2.3,and a thickness of the capping layer is in a range from 30 nm to 120 nm.5. The display device of claim 1, wherein a thickness of the fourthinorganic layer is in a range from 30 nm to 100 nm, and a thickness ofthe third inorganic layer is in a range from 400 nm to 2200 nm.
 6. Thedisplay device of claim 5, wherein: the fourth inorganic layer isinterposed between the third inorganic layer and the organic layer; arefractive index of the third inorganic layer is greater than arefractive index of the fourth inorganic layer; and the refractive indexof the fourth inorganic layer is between the refractive index of thethird inorganic layer and a refractive index of the organic layer. 7.The display device of claim 6, wherein the refractive index of thefourth inorganic layer satisfies:min (n1, n2) + |n2 - n1| × 0.25 < n3 < min (n1, n2) + |n2 - n1| × 0.75,where n3 represents the refractive index of the fourth inorganic layer,n1 represents the refractive index of the third inorganic layer, n2represents the refractive index of the organic layer, min(n1, n2)represents a minimum value of n1 or n2, and |n2 n1| represents anabsolute value of a difference between n2 and n1.
 8. The display deviceof claim 1, wherein the display element comprises light emitting diodes.9. The display device of claim 1, further comprising: a lower layerinterposed between the fourth inorganic layer and the organic layer,wherein the lower layer comprises an inorganic insulating material. 10.The display device of claim 9, wherein the lower layer directly contactsthe organic layer.
 11. The display device of claim 9, wherein: arefractive index of the fourth inorganic layer is greater than arefractive index of the organic layer, and a refractive index of thelower layer is between the refractive index of the fourth inorganiclayer and the refractive index of the organic layer.
 12. The displaydevice of claim 11, wherein the refractive index of the fourth inorganiclayer satisfies:min (n1, n2) + |n2 - n1| × 0.25 < n3 < min (n1, n2) + |n2 - n1| × 0.75,where n3 represents the refractive index of the fourth inorganic layer,n1 represents a refractive index of the third inorganic layer, n2represents the refractive index of the lower layer, min(n1, n2)represents a minimum value of n1 or n2, and |n2 -n1 represents anabsolute value of a difference between n2 and n1.
 13. The display deviceof claim 11, wherein: a difference between the refractive index of thelower layer and the refractive index of the organic layer is less than0.05.
 14. The display device of claim 13, wherein: the lower layer andthe fourth inorganic layer comprise an inorganic insulating materialcomprising a silicon element, a nitrogen element, and an oxygen element;and an oxygen content of the lower layer is greater than an oxygencontent of the fourth inorganic layer.
 15. The display device of claim1, wherein the third inorganic layer comprises a plurality of stackedfilms.
 16. The display device of claim 1, wherein the refractive indexof the second inorganic layer is smaller than the refractive index ofthe capping layer.